Due to safety considerations, it is beneficial for defects in the shift-control actuator to be recognized in every possible driving state, and preferably at a point in time early enough, for example, to prevent overlap shifting into incorrect gears that had been erroneously selected due to the defect. To this end, it is intended to ascertain the presence of a defect in the shift-control actuator on the basis of parameters acquired by the automated manual transmission, preferably before an erroneous overlap shifting occurs.